Rear tyre pressure

[ConanBarbarian]

I did some searching but was unable to find an explanation for dealer recommended rear tyre pressure being higher than the front.

Why would Skoda suggest to put 2 PSI more (light load) in the rear when almost 70% of the weight of the car is on the front axle? Should it help against saw-toothing?

 

The car is a MY07 (v)RS hatch.

Edited 3 November, 2014 by ConanBarbarian

[BlueVRSTom]

The only reason I can think of is the fuel tank is located at the back of the car?

But I don't actually know.

[vrsmatt1985]

I put 34 in back 32 in front

[robt100]

34 front 42 rear here Always carrying a boot full of things. Also helps economy

[brad1.8T]

Factory recomended pressures in front are too low IMO and aimed at comfort rather than good tyre life, handling or economy. Keep in mind that the pressure recommendation is a minimum.

I run 36psi all round. No passengers, nothing in the boot. Lots of motorway driving around 90-105kmh. Tyres get X-rotated every 10,000km. No saw-toothing.

[silver1011]

Keep in mind that the pressure recommendation is a minimum.

 

Really? Say's who?

 

I'd imagine the manufacturer would state the ideal pressures, not the minimum.

 

I would also expect them to prioritise safety (handling, braking etc.) and fuel economy over comfort when setting the pressures.

[Tall-Pete]

To answer ConanBarbarian's original, I would guess they are trying to balance up the naturally nose heavy understeer tendency. The harder rear tyre and lighter back end will bring the handling back towards oversteer - in this case only a little bit so you end up with mild understeer rather than heavy understeer.

[Guest]

The front tyres heat more than the rears because:

1. They flex more from the extra weight/lower initial pressure.

2. Have all the the engine power/braking going through them on a FWD car.

3. Generally have more braking force to contend with.

4. Are subject to cornering forces.

Add them all up and you get heat and the tyre pressure increases as a result.

If you inflated them to a higher pressure than 'recommended' they would overpressure when up to operating temperature and offer a harsher ride and possibly non optimal grip.

Of course higher pressures are required when you are heavily laden to prevent the tyres from being overly flexed and in so overheating and possibly failing in extreme cases.

There is a happy medium.

[brad1.8T]

 

Really? Say's who?

 

I'd imagine the manufacturer would state the ideal pressures, not the minimum.

 

I would also expect them to prioritise safety (handling, braking etc.) and fuel economy over comfort when setting the pressures.

 Most motoring associations & defensive driving schools. Plus the tyre manufacturers.

I worked in the tyre industry (Goodyear & others) for 8 years & that's what was drummed into us by the the guys in the tech department. One of the main factors affecting tyre failure at the time was under-inflation due to low factory pressure recommendation (note that word recommendation).

Pretty well any motoring association magazine article on tyres will say "always add a few extra psi" as will any defensive driving school. It's safer to be slightly over than under - you've got no guarantee the tyre inflator at the servo is accurate and it's more likely that a tyre will lose pressure than gain pressure unless it's overheating.

Skoda Octavia in particular is quite bad for it - how else do you explain that an Golf with less weight recommends more pressure in the tyres? It's because the Octavia is more oriented to comfort rather than responsive handling, maximum tyre life and optimum fuel consumption.

What pressures you run is your business but you're better over than dead-on IMO.

[brad1.8T]

 

If you inflated them to a higher pressure than 'recommended' they would overpressure when up to operating temperature and offer a harsher ride and possibly non optimal grip.

no they wouldn't.

If your tyres are at the optimal pressure for the type of driving you are doing then you'll get about 2-3 psi pressure increase when the tyre is up to operating temperature. This takes about 30-40 minutes when driven "normally" at about 20C (less if you are getting up it). If you're gaining more than 3psi then the tyres are under-inflated for the work they are doing & you should be running a bit higher pressure. My rule of thumb is that if you get a 4 psi increase then add another 2psi when cold & try again the next day.

[ConanBarbarian]

To answer ConanBarbarian's original, I would guess they are trying to balance up the naturally nose heavy understeer tendency. The harder rear tyre and lighter back end will bring the handling back towards oversteer - in this case only a little bit so you end up with mild understeer rather than heavy understeer.

What I find strange is that Skoda actually recommends less PSI in the rear than the front for the mk1 Superb (but higher overall pressures). The mk2 is a little different story though. (http://www.puretyre.co.uk/skoda-tyre-pressures/)

It's not my first car but all previous ones (front engine, FWD and 4WD) had lower pressure for the rear tyres suggested by the factory.

[silver1011]

I'd like to see these statements that suggest we should be running higher than the manufacturers recommendations.

 

I'm sure Skoda thought long and hard about what to print in the inside of their fuel filler flaps, as well as taking advice from their engineers and tyre suppliers.

 

To actively promote pressures lower than the ideal seems strange to me.

Edited 4 November, 2014 by silver1011

[kidology]

I run 34 all round as what my tyre fitter recommends, dont have any issues wear wise. 

[brad1.8T]

I'd like to see these statements that suggest we should be running higher than the manufacturers recommendations.

 

I'm sure Skoda thought long and hard about what to print in the inside of their fuel filler flaps, as well as taking advice from their engineers and tyre suppliers.

 

To actively promote pressures lower than the ideal seems strange to me.

I haven't got time to google for hours but:

3rd para 5th line

 

Yes, the manufacturers do think long & hard about the pressures but part of that is the target demographic of the vehicle & the predicted driving style of vehicle.  So an Octavia Elegance with 205/55r16 tyres has recommended pressures of 30F/32R but a vRS has recommended pressures for the same size tyre of 33F/39R.  The Elegance is expected (by the target demographic) to have a less sporty handling and a more comfortable ride than an RS owner would expect.  Golf R recommended pressures are 38 all round if i remember correctly but a vRS with the same 225/40r18 is 30F/33R which on the Skoda is basically asking for a sidewall rupture and flat-spotted rim if you hit a pothole at suburban speeds.

 

None of this is anything new or something that has been kept a secret.  Holden added 3psi to their recomended pressures a few years back so that they could improve fuel economy a fraction.  They openly admitted at the time that (paraphrased)  "we had previously tuned our tyre pressures to achieve a happy medium between ride comfort, tyre wear, handling & fuel economy.  We hope our customers will accept a slight loss in ride comfort and appreciate the benefit of extra fuel economy, tyre life & handling response that the higher tyre pressures give".

 

The other thing you have to keep in mind is that the service station pumps are allowed +-2psi so there's a possibility that the 30psi you put in the front is actually 28psi.  Slight over-inflation has almost no downside but under-inflation is very dangerous.

 

Do what you want but maybe as an experiment give 34psi all-round a shot for 3000km.  You might be surprised how good it feels & there's no downside unless you like a super-plush ride.

Edited 5 November, 2014 by brad1.8T

[ConanBarbarian]

So an Octavia Elegance with 205/55r16 tyres has recommended pressures of 30F/32R but a vRS has recommended pressures for the same size tyre of 33F/39R.  The Elegance is expected (by the target demographic) to have a less sporty handling and a more comfortable ride than an RS owner would expect.  Golf R recommended pressures are 38 all round if i remember correctly but a vRS with the same 225/40r18 is 30F/33R which on the Skoda is basically asking for a sidewall rupture and flat-spotted rim if you hit a pothole at suburban speeds.

Where did you obtain recommended R16 tyre pressures for the vRS? My fuel flap only has readings for R17 an R18.

Also what's your take on Skoda suggesting more air in the rear (or less in the front, depending on how you put it)? Do you agree with the idea that a front heavy car should have more pressure in the front (compared to rear) tyres? I assume you don't based on your 'I run 36psi all round' statement

[brad1.8T]

Where did you obtain recommended R16 tyre pressures for the vRS? My fuel flap only has readings for R17 an R18.

Also what's your take on Skoda suggesting more air in the rear (or less in the front, depending on how you put it)? Do you agree with the idea that a front heavy car should have more pressure in the front (compared to rear) tyres? I assume you don't based on your 'I run 36psi all round' statement

 

From a discussion we were having about tyre pressures at VWWC a while back.  I found the image googling but of course, can't find it today.  Feel free to call BS on it as I can't show the evidence but it was at VWWC.

 

Just to confuse the issue, here's another one with totally different pressure (32F/30R) that I found while trying to find the original image.  WTF?

 

Tall-Pete in post #7  gave a really good explanation why they might do it (higher pressure rear makes it feel like it understeers less).  Possibly the lower front pressure would give more ultimate grip but the turn-in wouldn't be as crisp and it would also tend to hang-on, hang-on, hang-on & bang! let go.  I prefer a well telegraphed & gradual break-away.

 

It comes down to personal preference I guess.  I prefer good turn-in over ultimate grip & I like my tyres to last a long time & get good economy.  I usually (eventually) set my cars up quite stiff with sports style dampers & slightly harder springs so having a compliant sidewall on minimum pressure doesn't work in harmony with that.

 

I'm not conservative when it comes to sticking with factory settings as a lot of my work (back in the day) as a wheel alignment specialist meant I had to throw the factory settings out the window & come up with something that worked to fix a problem.  Part of that was fiddling with tyre pressures on various makes where the manufacturer had got it totally wrong (Toyota Tarago and Izuzu/Holden Gemini spring to mind - both needed 10psi extra over the recommended to stop edge wear.)

 

I also worked / volunteered for a season with a major touring car team (RX7s) helping with tyres, tyre changes, temperature measuring, etc and those old guys taught me a lot about the change it / test it / change it process and don't just do what everyone else is doing (We ran Goodyear wets when everyone else was running Dunlop wets and the pressures & alignment settings were totally different).

 

This car but different livery

 

So yes, I like to try different things & they don't always work as expected.

[SkodaKitteh]

It's funny this subject should come up because just days after getting my vRS my neighbour came up to me and said your tyres look a bit low on pressure.  That happened again, with a different person only recently !  I check them regularly and go with the recommended pressures but I do think the tyres look slightly under-pressure on the vRS.  I might try adding 2 or 3 psi and see if it makes any difference.

Edited 6 November, 2014 by SkodaKitteh

[J306TD]

Had my rears balanced yesterday. Spoke to the guys about tyre pressure. They said 32 front and 34 rear is what they would set them too

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[Bishman]

I use 36 PSI all round and inflate them once a month.  Doing about 250 miles a week they tend to lose 1 or 2 PSI  every month I find.